This application claims priority under 35 USC xc2xa7119 to Japanese Patent Application No. 11-309013 filed on Oct. 29, 1999, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention generally relates to an image forming apparatus, such as a copier, a printer, a facsimile, a duplicator, and a combined machine combining these image-forming apparatuses, and in particular relates to a rotation member driving apparatus for use in the image forming apparatus.
2. Discussion of the Background Art
It is well known, in an image-forming apparatus having a drum shaped photo-conductive member (hereinafter referred to as a PC drum), that the PC drum and its peripheral units are made into a single unit detachable in relation to an essential structure of the image forming apparatus (hereinafter simply referred to as a body). Such a detaching operation is generally performed as a countermeasure against fatigue made by time elapsing of the PC drum each time when, e.g., a unit of 100 thousand of image formations has been made to replace with a new PC drum unit. To improve performance of the detaching operation, the following background rotating member-driving apparatus illustrated in FIGS. 7 through 11 is generally utilized.
As illustrated in FIG. 9, the PC drum 1 is configured to be cylindrical. The right side of the PC drum 1 should be a rear side of the body, and the left side thereof should be a front side of the body. A flange 2 is integrally provided to support an end of the PC drum 1. A driving shaft guiding hole 3 is provided to penetrate the flange 2. A guiding hole 4 having a diameter larger than the driving shaft-guiding hole 3 is provided in the vicinity and at the right side of the driving shaft-guiding hole 3.
A separation wall is provided as a border between the driving shaft guiding hole 3 and the guiding hole 4. Four convex portions 5 and four concave portions 6 are each respectively disposed on a cross at the guiding hole 4 side of the separation wall. The four convex portions 5 and the four concave portions 6 collectively constitute a driving force receiving joint 11 as claimed.
A PC drum unit (not shown) pivotally supports the PC drum 1 at the end of the front side of the PC drum 1. The PC drum unit is detachably attached to the body from the front side to the rear side (not shown) of the body. When the PC drum unit is attached to the body, a rotational motive power of the driving shaft 7 can be transmitted to the flange 2, then to the PC drum 1.
As illustrated in FIG. 7, a penetrating hole 9 is formed in the driving shaft 7 at the vicinity of the front side end of the driving shaft 7, and penetrates in a direction of the diameter of the driving shaft 7. As illustrated in FIGS. 8A and 7, a driving force transferring member 10 is attached to the driving shaft 7 as described earlier. The driving force transferring member 10 is formed almost in a cylindrical shape and is slides to fit with the driving shaft 7.
Continuing with FIG. 8A, a driving side joint 12 is formed at the front side end of the driving force transferring member 10. Four convex portions 15 and four concave portions 14 are formed on the driving side joint 12 on a circumference concentric with the driving force transferring member 10 and disposed respectively on a cross. Thus, these four convex portions 14 and the four concave portions 15 can mesh with the corresponding convex portions 5 and concave portions 6, of FIG. 9.
Back to FIG. 7, an oblong hole 16 is formed on another side of the driving force transferring member 10 in the vicinity of the driving side joint 12. Thus, when assembling the driving force transferring member 10 to the driving shaft 7, the driving force transferring member 10, and, the driving side joint 12 are fitted with the driving shaft 7. The driving force transferring member 10 is directed to the rear side of the body. The oblong hole 16 is then positioned above the penetrating hole 9. A spring pin 8 is inserted into both the oblong hole 16 and the penetrating hole 9 with pressure.
In FIGS. 8A, 8B, and 8C, the shorter diameter of the oblong hole 16 is represented by W1. A diameter of the spring pin 8 is represented by D1. The diameter D1 should be measured in a diameter changeable direction by including a split portion 8a in the condition that a force is not applied to the spring pin 8. A diameter perpendicular to the diameter D1 is represented by D2. In this example, each diameter is predetermined as follows.
D2=1.95 mm
D1=2.15 mm
W1=2.1 through 2.2 mm
When the spring pin 8 is to be inserted into the penetrating hole 9 through the oblong hole 16, the spring pin 8 is inserted with the slot portion being engaged with the oblong hole 16. Thus, impediment to be produced when the insertion is made can be relatively reduced.
Thus, the driving force transferring member 10 can slide while being guided by the spring pin 8 during a stroke of the oblong hole 16. In addition, the driving force transferring member 10 can move under the condition where the spring pin 8 fitting into the oblong hole deforms as little as possible in the direction in parallel to the shorter diameter W1. The oblong hole 16 has both ends each having a curvature fitting with an outer surface of the spring pin 8 to improve contacting efficiency of the spring pin 8 when the spring pin 8 contacts the end. A protruding portion of the spring pin 8 protruding from the driving shaft 7 is designed with nearly the same thickness of the cylinder of the driving force transferring member 10.
Referring to FIG. 7, when the driving force transferring member 10 is assembled to the driving shaft 7, a coil spring 17 is set around both of the driving shaft 7 and the driving force transferring member from the rear side of the driving shaft 7, and, accordingly, the driving force transferring member. An E-shaped ring 18 is attached to a groove 19 formed around the driving shaft 7 while the front end of the coil spring 17 contacts the joint 15 and the rear side of the coil spring pin 17 is positioned at the front side than the groove 18.
Thus, the E-shaped ring 18 can stop the rear side of the coil spring 17, and, as a result, the coil spring 17 engages the driving force transferring member 12. Thus, the driving force transferring member 12 is always biased to the front side of the body.
When no force is applied to the driving force transferring member 12, one end of the oblong hole 16, i.e., the end of the rear side of the oblong hole 16, contacts the spring pin 8 with some bias made by the coil spring 17 as illustrated in FIG. 9. Conversely, if any force directing to the rear side of the body is applied to the driving force transferring member 10, the spring pin 8 changes its position to the other end of the oblong hole 16, i.e., the front side of the body, or in the vicinity thereof as illustrated in FIG. 2.
Thus, movement of the driving force transferring member 10 ranges from a position where one end (not shown) of the oblong hole 16 contacts the spring pin 8 to a position where the other end of the oblong hole 16 contacts the spring pin 8.
In FIG. 9, the driving shaft 7 is supported by the apparatus body (not shown) at its rear side end so as not to be displaced either toward the front side or the rear side of the body. The driving shaft 7 is engaged with a driving motor via gears of driving force transmitting power as mentioned later.
Still referring to FIG. 9, when the PC drum 1 is to be attached to the driving shaft 7, an operator firstly lifts the PC drum 1 together with the PC drum unit (not shown). The operator inserts the same toward the rear side of the body in a manner that an axis of the driving shaft-guiding hole 3 substantially accords with that of the driving shaft 7. The operator further pushes the PC drum unit in a direction as shown by an arrow 20 until the PC drum unit reaches a stopper (not shown) while a tapered portion 7a formed at a leading end of the driving shaft 7 engages with the guiding hole 4.
Further, the tapered portion 7a is lead toward the driving shaft guiding hole 3 via the guiding hole 4, and a position of the PC drum unit is fixed at a predefined position. A securing member (not shown) then secures the PC drum unit. At that time, the convex portions 15 and the concave portions 14 are inserted and each respectively engages with the corresponding concave portions 5 and the convex portions 6 with the bias of the coil spring 17. Thus, a rotational force of the driving shaft 7 can be transmitted to the PC drum 1 via the engagement.
To make the engagement smooth, a width of each convex portion 15 is designed to be smaller than that of each concave portion 6, and width of each concave portion 6 is also designed to be larger than that of each convex portion 15. In addition, to facilitate a meshing operation, a tapered portion 115 is formed at a leading end of each convex portion in such a manner that the closer to its leading edge the smaller in diameter, and a tapered portion is also formed at a bottom of each concave portion in such a manner that deeper the narrower.
If the operator simply attaches the PC drum 1 together with the PC unit to the apparatus body, both the concave portions 14 and the convex portions 15 do not precisely accord with the corresponding convex portions 5 and the concave portions 6, respectively, at the beginning of the meshing operation. For example, as illustrated in FIG. 10, an entrance of each convex portion 14 collides with a leading end of each convex portion 5, and the meshing is impossible.
To prevent such a problem, the driving shaft 7 executes idling rotation when the driving side joint 12 is separated from the driving force receiving side joint 11. In addition, the driving force transferring member 10 is moved toward the front side of the body by elastic pressure made by the coil spring 17 at first when both of the concave portions 14 and the convex portions 15 are aligned with the corresponding convex portions 5 and the concave portions 6, respectively. As a result, the concave portions 14 and the convex portions 15 can automatically be aligned with the convex portions 5 and the concave portions 6, respectively, as illustrated in FIG. 11.
Thus, to automatically execute the meshing operation, the driving force transferring member 10 is designed to move in the direction in parallel to the driving shaft 7 within the longitudinal range of the oblong hole 16 as mentioned above. Namely, the driving force transferring member 10 is moved toward the rear side of the body by the driving force receiving side joint 11 to deviate from a normal meshing position, when a portion of one of the convex portions 15 contacts a portion of one of the convex portion 5 at a position. When the concave portions 14 and the convex portions 15 are aligned with the convex portions 5 and the concave portions 6, respectively, the driving force transferring member 10 is moved to the front side of the body by the bias of the coil spring 17.
The flange 2 where the driving force receiving side joint 11 is located, the driving force transferring member 10 where the driving side joint 12 is located, the spring pin 8, the oblong hole 16, the coil spring 17, and the E-shaped ring 18 and related structure collectively constitutes the rotation member driving apparatus as claimed.
When the concave portions 14 and the convex portions 15 mesh with the convex portions 5 and the concave portions 6, respectively, the spring pin 8 positions at the front side end of the oblong hole 16 as illustrated in FIG. 11. In this state, a gap between the shorter diameter W1 of the oblong hole 16 and the spring pin 8 is designed as small as possible, as shown in FIG. 8A. That is, if the gap is large enough, the gap generally introduces vibration of the PC drum 1, and resulting in generating jitter on an image formed on the PC drum 1.
To avoid the above-noted problem, a curved portion of one end, i.e., the end of the front side of the oblong hole 16 of the background art is designed to contact the spring pin 23 so that the amount of gap therebetween is substantially zero. Since a backlash occurs between the driving force transferring member 10 and the driving shaft 7 due to the gap, the difference between the shorter diameter W1 of the oblong hole 16 and a diameter of the spring pin 8 is designed as small as possible. In addition, the rear side end of the oblong hole 16 is also made with a prescribed curvature to improve the contacting efficiency of the spring pin 8.
However, if the contacting efficiency is highly improved, and when the idling rotation is performed, and, accordingly, the driving force transferring member 10 is going to be moved toward the front side of the body with the bias of the coil spring 17, the driving force transferring member 10 sometimes can not move because the friction of the spring pin 8 in relation to the oblong hole 16 is too high to be able to slide. As a result, the above-mentioned meshing condition can not correctly be established, and the PC drum 1 is not driven. Thereby, the image formation is impossible.
The above-mentioned example assumes that the structure in which the PC drum is held is in the PC drum unit. However, the same problem occurs when a PC drum is solely detached to the apparatus body.
The present invention has been made in view of such problems and to address and resolve such problems. Accordingly, it is an object of the present invention to provide a novel rotating apparatus for rotating, by transferring a driving force generated by a motor disposed in a body, a rotation member detachable from the body. A driving shaft disposed in the body may transfer the driving force by rotating itself in a prescribed direction. A driving force receiving device may be disposed in the rotation member and has a driving force receiving joint configured to receive the driving force. A driving force transferring device may be engaged with the driving shaft and includes a driving force transferring joint configured to engage with the driving force receiving joint.
The driving force transferring device may transfer the driving force from the driving shaft to the rotation member. A moving member may move the driving force transferring device back and forth along the driving shaft so as to engage and disengage the driving force transmitting joint respectively with the driving force receiving joint when the driving force receiving device contacts the driving force transferring device. A guiding member may be provided at least one of the driving shaft and the driving force transferring device. A camshaft may be provided on at least another one of the driving shaft and the driving force transferring device, and may fit into the guiding member. The camshaft may nearly contact one end of the guiding member when the driving force receiving joint engage with the driving force transferring joint. The cam shaft may nearly contact another end of the guiding member when the driving force transferring joint is separated from the driving force receiving joint and positioned at it initial position. A fitting level of the camshaft in relation to the guiding member is strict at around the one end, and is loose at around the other end.